In general, a magnetic recording medium such as a magnetic tape is produced by coating and drying a magnetic paint comprising a ferromagnetic powder and a binder on a nonmagnetic support.
In a magnetic recording medium, particularly a magnetic recording medium for video use which requires a high-frequency recording, there has lately been a demand for increasing the recording density. With the demand for higher-density recording, a further finer particulate and high-coercive ferromagnetic powder having a specific surface area of 45 m.sup.2 /g has come into use.
However, as the ferromagnetic powder becomes finer particulate and highly coercive, its individual particles are liable to strongly aggregate, which makes it difficult to provide any sufficient dispersibility and surface smoothness necessary for obtaining a high reproduction output and good S/N ratio in the high-frequency recording. This tendency is remarkable particularly in a ferromagnetic metal powder.
With the recent development of high-functional video tape recorders, most of them are now of the multihead type, which causes a jitter broblem called head rapping, so that there has been a strong demand for the stabilization of video tape running.
Under such circumstances, many attempts have now been made to improve magnetic recording mediums by removing therefrom their shortcoming that making a ferromagnetic powder fine particulate reduces its dispersibility. For example, Japanese Patent Publication Open to Public Inspection (hereinafter referred to as Japanese Patent O.P.I. Publication) No. 57527/-1985 discloses techniques for improving the dispersibility of a ferromagnetic powder by incorporating into the magnetic layer a modified polyurethane containing a functional group selected from the group consisting of a carboxyl group, hydroxyl group, sulfonic acid group and epoxy group.
According to our investigation, however, only the use of a polyurethane containing a polar functional group, even though it can improve the dispersibility of the magnetic powder, have difficulty in obtaining a tape run stable enough to restrain the head rapping.